Paper manufacture



Feb. 2, 1932. J. TRAQUAIR ET AL PAPER MANUFACTURE Filed Dec. 29, 1928 2 Sheets-Sheet INVENTOR A TTORNEV-S Patented Feb. 2; 1932 UNITED STATES.

PATENT OFFICE JOHN TRAQUAIR AND FRANCIS G. RAWLING, 0F CHILLICOTHE, OHIO, ASSIGNORS TO THE HEAD RESEARCH ENGINEERING COMPANY, OF DAYTON, OHIO, A CORPORATION OF OHIO PAPER, MANUFACTURE Application filed December 29, 1928.

tion is to provide a method of treating fibrous materials to produce a superior pulp product which may be formed into paper having strength, color and other characteristics superior to the corresponding characteristics in paper formed from thesame fibrous materials in other generally known ways previously used.

Another object of the invention is to pro vide a method of treating hard deciduous wood, such for example as chestnut, to produce a white pulp product of good color and high strength suitable for the manufacture of high grade paper, such as printing paper.

Another object of the invention is to provide a superior white or bleached pulp product having exceptionally good color and high strength and possessing unusual felting and clay-carrying qualities.

Still another object of the invention is to provide apparatus for carrying out the above method and for producing the above product.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and appended claims.

In the drawings in which like characters of reference designate like parts throughout the several views thereof--- Fig. 1 is a diagrammatic side elevational view of a portion of a preferred embodiment of apparatus constructed for carrying out the method of this invention; and

Fig. 1 is a diagrammatic side elevational view of another portion of the apparatus, Figs. 1 and 1 when placed and to end disclosing the complete apparatus.

The present invention provides a method of treating fibrous materials of various kinds, such as various types of wood, straw, fibrous grasses, and the like, to produce a finished pulp product of exceptionally high white color and high strength, with yields considerably higher than those heretofore obtained Serial No. 329,081.

in the manufacture of white pulps with the known pulping processes. The method of this invention is especially adapted for the treatment of hard deciduous or non-resinous broad-leafed wood, such as chestnut, oak, gum, and the like, to form a superior white or bleached pulp product. Thls invention thus makes available, for the manufacture of high grade paper, waste wood from wood working and furniture factories, and the like. This waste wood has not heretofore been commercially available with the known pulping processes, because it generally contains a percentage of very resistant hard woods such as oak, walnut, mahogany, and the like, which shows up in the final pulp as unbleachable fibers and hard fiber bundles or shives. This raw material is a very cheap and abundant source of supply of cellulose, being generally available at a cost which is only slightly in excess of its fuel value, and is in excellent condition for the manufacture of high grade pulp inasmuch as the raw material is generally clean, dry and sound. The invention also makes available for the manufacture of high grade pulp other waste wood supplies, such as leached chestnut chips from tannin extract mills, cull lumber, wood shavings, saw mill waste, and the like.

In accordance with the method of this invention, the fibrous material is first subjected to an incomplete chemical digestion under such conditions of temperature and pressure and of concentration and character of chemical as to loosen and soften the bonding material holding the fibers in their natural associated form, without materially affecting the cellulose and while maintaining the strength a of the fibers. In this chemical treatment, the cooking or digestion, which is effective to soften the bonding material holding the fibers together, is purposedly so limited in its effects that considerable defibering or separating of the fibrous material into its ultimate fibers does not result, and there is a resulting high strength and yield of the-ultimate prodnet. The partially defibered material is then subjected to a multistage and coordinated chlorination treatment to complete the pulping or disintegration thereof, the chlorination treatment being carried out so as to prevent injury to the cellulose fibers, maintain the high strength of the ultimate product and secure a good yield. For purposes of illustrating a preferred embodiment of the method, the invention is hereinafter described in connection with the treatment of hard deciduous wood, such as leached chestnut chips from which tannic acid has been extracted.

Referring to the drawings, a conventional chip breaker or hog is indicated at 10 which serves to subdivide the logs or pieces of wood into chips of suitable size, such as a size suitable for boiler fuel. If a supply of chips is available, such as leached chestnut chips, a chip storage may replace the chip breaker. The chips are fed by a conveyor 11 into a feeding hopper 12 which discharges into a digester indicated at 13. This may be a conventional digester, such as a stationary, rotary or tumbling digester, having a feeding opening 14 closed by a removable cover 15 and a conical discharge end 16 provided with a discharge valve 17. A steam supply pipe 18 is provided, which may be connected as shown for a stationary digester, or connected through the trunnions in a rotating or tumbling type of digester. Cooking liquor is supplied from a tank 23 through a pipe 24 controlled by a valve 25.

The chips are subjected in the digester 13 to what is termed an incomplete digestion.

- This is so controlled that the chips retain substantially their original form, but may thereafter be readily defibered with properly coordinated mechanical and chemical treatments. This incomplete digestion may vary considerably, depending upon the fibrous material being treated and the ultimate product desired. As an example of such an incom plete digestion, a so-called semi-chemical cook is hereinafter more fully described. This serves to soften the adhering incrustants, such as lignins, holding the fibers together without dissolving a large proportion of these incrustants and without deleteriously affecting the cellulose, thereby giving high yields and high strength. Very satisfactory results are secured with a cooking liquor comprising an aqueous solution of an alkali metal sulphite containing a salt of a weakly ionized polyhasic acid, such as a mixture of sodium sulphite and sodium bicarbonate. ther alkali metal sulphites, such as potassium sulphite, and other salts of weakly ionized polybasic acids, such as alkali metal carbonates, tartrates, citrates, borates, oxalates, and the like, may be used.

The cook is carried out in stages. In practice, the cover 15 of the digester 13 is removed and chips are fed by the conveyor 11 into the digester until the required charge is introduced. Steam is then introduced for a short period of time by the pipe 18 to heat up the material to facilitate impregnation. The

valve 25 is then opened and a controlled quantity of cooking liquor of controlled concentration is fed into the digester. The tank 23 may be positioned at a sufficient height to permit the liquor to feed in by gravity, or a pump may be used. Steam is then introduced into the mixed mass to raise the temperature to about 125 C. to 150 C. for a period of time, generally about one hour to two hours, to secure. impregnation of the liquor throughout the individual chips. The valve 25 is then opened, and the unabsorbed liquor within the digester is forced back into the tank 23 by means of steam pressure existing within the digester. A portion'of the liquor is retained or absorbed by the chips within the digester. The liquor returned to the tank 23 is partially exhausted by reaction during the impregnation stage. Fresh concentrated makeup liquor is supplied from a tank 27 through pipe 28 to the tank 23 to make up the volume and concentration of the liquor within the tank 23 to provide cooking liquor for a subsequent charge.

The chips with absorbed liquor are then steamed to bring the temperature within the digester up to about 160 C. to 180 C. or higher, and to a high pressure, for a period of time to secure the desired reaction of the liquor With the lignins and other bonding materials to secure the softening of the chips. According to the length of time and temperature of this reaction stage heating treatment, the characteristics of the cooked material are determined, such as whether it can be easily hydrated or not, its bulkiness, and the degree of hardness or softness of the cook. Satisfactory results are secured with a treating time in this reaction stage of about one to four hours.

When the cooking liquor within the digester is maintained approximately neutral still better results are obtained, the lignins being effectively resolved or softened While the cellulose is substantially uninjured. Highly satisfactory results are secured when the pH value of the solution is maintained between 5 and 9. During the cooking, pyroligneous acids are liberated from the Wood which tend to render the cooking liquor acid in character. The presence of the alkali salt of a Weakly ionized polybasic acid, such as sodium bicarbonate, effects the neutralization of these acids as formed. In order to neutralize any alkalinity resulting from hydrolysis of the sodium salts producing caustic soda, an excess of carbon dioxide gas is preferable during the cooking operation, this forming carbonic acid within the digester and reacting with the canstic soda as it forms to produce sodium bicarbonate which is substantially neutral in aqueous solution. As the carbonic acid is an extremely weak acid and as it is only ionized to a slight degree in the cooking liquor, it serves both the impregnation and reaction stages.

The control of the neutrality of the cooking liquor'may be easily accomplished by noting the temperature and pressure conditions within the digester. If steam alone is illjected into a digester and other gases or vapors are absent, a definite pressure is obtained at any definite temperature. By the introduction of carbon dioxide gas, a still higher pressure isobtained at any definite temperature than is obtained with steam alone. Vhen a bicarbonate containing cooking liquor, such as sodium bicarbonate, is used, a certain amount of decomposition of the chemical with the formation of CO gas results, so that the pressure obtained within a digester with such a cooking liquor is 'due not only to steam pressure but also to false pressure of the carbon dioxide gas resulting from the decomposition of the bicarbonate. By running a series of tests to determine the degree of decomposition of a sodium bicarbonate solution at higher temperatures, a temperaturepressure chart may be plotted which will indicate the pressure which should be obtained within the digester at any temperature when bicarbonate is present. In operation, the actual pressure in the digester may be maintained slightly above this calculated pressure for any given temperature by the introduction of excess CO gas through the pipe 30. If the pressure within the digester falls below the predetermined normal for any given temperature, manipulation of the valve 31 toward opening position will restore the desired conditions within the digester. Should the actual pressure recorded in the digester rise above predetermined normal for any given temperature, the digester is relieved by allowing some of the gas to escape through the pressure relief valve 32. A control chart may be provided for the digester, and the control of the cooking conditions within-the digester effected by proper manipulation of the valves controlling the introduction of steam and carbon dioxide in accordance with variations in pressure from the desired predetermined normal as indicated on the chart for any particular temperature.

The cooked material is discharged from the digester 13 into a dump tank 35. The material at the completion of the cooking is softened but still maintains to a large degree its shape. To facilitate the subsequent handling of this material the digester is preferably not blown, but is merely dumped so that the softened material is not shredded or pulped at this stage, but is maintained in chip form. The mass of softened chips discharged into the dump tank 35 is then washed to remove residual liquor. The washing may be performed by the introduction of wash water through pipe 38 onto the surface of the chips within the dump tank. These chips are sup ported upon a perforated bottom, which may be a'lattice-work as indicated at 36, the washing liquor draining through the lattice-work and escaping to recovery through pipe 37.

The dump tank 35 is provided with means for feeding the softened and drained chips at a controlled rate to a mechanical disintegrator. As illustrated the bottom of the dump tank is provided with an opening 40 located adjacent the periphery of the tank. This opening is closed by a sliding valve 41 during the dumping and washing operations, and is then opened to permit the feeding of softened chips at a controlled rateonto an endless conveyor 42. Positioned within the dump tank is a leach caster, which comprises a central vertical shaft 45 supported in suitable bearings and driven'through gears 46 and 47 from a drive shaft 48, which in turn is driven at a controlled and variable rate from any suitable source of power. A stirring arm 50 is slidably mounted on the shaft 45 for vertical movement thereon and is keyed to the shaft so as to rotate therewith. The arm carries a plurality of inclined blades or fingers 51 which are so inclined as to move the chips toward the periphery of the tank upon rotation of the shaft 45 and arm 50. The arm 50 is rotatably supported by a thrust-bearing 52 carried by a non-rotatable cross beam 53 which is suspended by cables 54 from a winding drum (not shown) which is adapted to be rotated in opposite directions through suitable conventional driving machinery (not shown) at variable speeds to lower or raise the stirring arm 50 in accordance with the level of the chips within the tank 35, so that the arm 50 operates upon the upper surface of the chips. The rate at which the chips are fed to the periphery of the tank is controlled by the rate of rotation of the shaft 45, or by the rate of lowering of the arm 50, this in turn controlling the rate at which the chips are fed through an opening 39 in the lattice work 36 and the aligned opening 40 onto the conveyor 42.

The conveyor 42 discharges the chips into a receiving hopper 55 feeding into an end-' less bucket elevator 56, which in turn discharges onto an endless conveyor 57 feeding into an inlet 58 of a rod mill 60. Any suitable type of mechanical disintegrator can be used to disintegrate the softened chips at this point to prepare them for subsequent treatment, examples of other suitable mechanical disintegrators being centrifugal type mills such as Bauer mills, swinghammer type mills, edgerunner mills and the like. A controlled supply of dilution liquor, which is preferably white water from a paper forming machine where this is available, is admitted concomitantly with the softened chips through a supply pipe 62. The dilution liquor is generally controlled to provide a stock consistency of about 5% to 8% within the rod mill.

The rod mill comprises an outer rotary shell 63 which contains therein a plurality of loose parallelly arranged rods extending substantially throughout the length of the shell. The contracted ends 58 and 64 of the shell are supported in suitable bearings (not shown) and the body of the shell is provided with an annular gear 65 which is driven through gearing from a suitable power shaft (not shown). The softened chips are simultaneously fed into the inlet 58 with dilution liquid from pipe 62, and the stock feeds from the inlet 58 to the discharge 64: as the casing 63 is rotated to thereby give a thorough pounding, rubbing and shredding treatment to the fibrous material which servesto reduce the softened chips and to hydrate the fibers without objectionable cutting of the fibers, to thereby directly expose the small particles or hard fiber bundles or shives to facilitate the subsequent chlorination. In disintegrating mills of this character provided with loose or swinging impacting elements, the unreduced bundles or lumps of fibrous material receive substantially the entire action of the movable elements, such as the rods, while the portions that are sufficiently reduced are protected by the lumps against further reduction and cutting action. The rod mill has a certain definite capacity and the fibrous material feeds in until the mill is properly filled, or until the treated stock begins to overflow from the discharge end 64. The discharge from the mill then proceeds in accordance with the rate at which fresh mate rial is fed into the mill, the time of treatment within the rod mill being thereby controlled by the rate of feed.

The material discharged through the end 64 of the rod mill feeds into a stock chest 68 provided with suitable agitatifig mechanism, such as a driven shaft 69 having agitating blades 70. At this point additional dilu tion liquid, such as white water, is added through a pipe 71 to reduce the consistency of the stock within the chest 68 to a point such that it can be readily pumped through conduits, a consistency range of about 3% to 5% giving satisfactory results. Stock is withdrawn from the chest 68 through pipe 72 by a suitable pump such as a centrifugal pump 73, which feeds it through a pipe 7 1 to the central compartment 75 of a conventional head box 76.

As shown, the box 76 is divided by partitions 77' and 78 into outer compartments 79 and 80 and central compartment 75. The compartment 79 is connected by pipe 81 with the stock chest 68, whereby the excess of stock pumped to the head box and overflowing the partition 77 is returned to the stock chest 68. The compartment 80 is connected by pipe 82 to a conventional mixing box 83. The partition 78 is provided with an adjustable gate or weir 84 which serves to provide for the feeding of a controlled amount of stock to the mixing box 83. The mixing box has a plurality of staggered bafiies 85 to effect a thorough mixing of the stock and additional dilu tion liquor introduced by a pipe 86, this serving to further reduce the consistency of the stock to a point most effective for screening and filtering, such as about 1% to 2%.

The stock discharges from the mixing box 83 through pipe 87 into a conventional coarse screen or knotter screen, illustrated as a rotary screen 90. This comprises an outer confining casing 91 within which is rotatably mounted a spaced cylindrical screen 92. The stock feeds from the pipe 87 into the interior of the rotary screen, the meshes of which are sufficiently large to permit the material which has been sufficiently defibered and the dilution liquor to pass therethrough into the outer confining casing 91 from where it discharges through pipe 93. The larger undefibered particles, lumps and knots which do not pass through the screen are discharged at the end onto a suitable conveyor 94, or otherwise collected, for the purpose of feeding them back into the inlet 58 of the rod mill 60, whereby the tailings are returned to the system for further reduction.

The screened material discharges from the pipe 93 into a continuous filter mechanism 95 which serves to wash and thicken the treated material. This filter mechanism may be a conventional rotary vacuum filter such as an Oliver filter. This comprises a cylindrical rotary screen 96 divided into compartments of definite suction areas. The screen dips into the stock confined within a tank 97 into which the stock from the pipe 93 discharges. Suction within the compartments of the screen causes the fibrous mate rial to accumulate on the surface of the screen as the water passes therethrough into the suction compartments. As the screen rotates carrying the filtered fibrous mat above the liquid level in the tank, a supply of wash water is directed upon the mat from supply pipes 98. This serves to remove any remaining cooking liquor from the material. As the filter continues to rotate, the mat which has thus been washed and thickened arrives at an area which is not subject to suction, and at this point a flexible scraper member 99 scrapes the material from the filter into a chute 100 which discharges into a stock chest 102 similar to the stock chest 68. The chest 102 has an agitator 103 and a pipe 104 for the introduction of dilution liquor. A pump 105 serves to withdraw the stock V The overflow pumped to the head box 108 is returned by pipe 109 to the stock chest 102, and a controlled quantity of the stock passes by pipe 110 to the chlorination apparatus where the disintegration of the fibrous material into pulp is completed.

A controlled supply of chlorinating agent such as chlorine water or chlorine gas is introduced into the stream of fibrous material by pipe 111 controlled by valve 112. The stock may be made down to low consistency in the stock chest 102, or the chlorine water may be quite dilute to additionally lower the consistency of the stock such that objectionable temperature rise of the diluted mass in the initial chlorination is avoided. In dilute consistency, the water in which the fibers are suspended apparently serves as a heat-absor ing medium, serving to prevent an objectionable temperature rise of the mass due to the chlorination, and also serving to di lute hydrochloric acid formed in the reaction, this additionally diminishing objectionable results. Very satisfactory results have been secured with consistencies below 5%. Such low consistencies provide a fluid mass that may be readily flowed or pumped through conduits or treating chambers. The fibrous mass and chlorinating agent pass together into a mixer 113 which comprises a length of pipe having a spiral baffle 114 therein to create turbulence in the flowing stock stream to mix the chlorinating agent with the mass. The mixed mass then passes into the chlorinating tank or chamber 115 which is constructed of acid-proof material such as tile or the like and is divided into a plurality of connected chambers, represented in the drawing by two chambers 116 and 117 divided by a central partition 118 terminating short of the bottom of the tank. The mixed mass and chlorinating agent flow downwardly through the space 116 and beneath the lower end of the partition 118, and up through the space 117 to the overflow pipe 120. w

The tank 115 is constructed of a capacity to accommodate sufficient material to provide the desired reaction time as the stock flows from the inlet to the outlet. In this manner, a continuous chlorination is effected as the mass flows along. The amount of chlorinating agent is continuously controlled by the valve 112, preferably in an amount insufficient for complete chlorination. As a result, the more readily chlorinated material first reacts with the chlorinating agent in a comparatively short time as the mass flows along. The amount of chlorinating agent, however, is preferably controlled to be as much as will be readily taken up by the fibers 'in this short treating period, while insuring substantially complete reaction. This initial reaction is rapid, and it has been ascertained that the reaction of about of the chlorine required for complete chlorination of a given fibrous mass goes to substantial completion in about 15 to 20 minutes. Generally the addition of about 65% to of the chlorine needed for complete chlorination in this first I stage with a treating time of about half an hour gives very satisfactory results. I Various reagents may be used for this first stage, such as chlorine, sodium hypochlorite, bromine and the like, which for purposes of description are herein termed chlorinating agents. Chlorine is preferred due to the ease of control, effectiveness and rapidity of reaction, and lesser cost of the chemical. However, the use of ordinary bleach liquor or other calcium compounds at this point is not so satisfactory, due to the formation of ins soluble calcium compounds in the pulp which are not readily washed out in subsequent washing treatments. At this stage, the chlorine may be added in a roughly controlled amount sufficient to effect this initial chlorination, and this is usually done by adding chlorine water of a strength andin an amount to dilute the stock to the desired low consistency and to preferably provide an amount insufiicient for complete chlorination within the limits above mentioned. The addition of chlorine is in practice controlled according to the characteristics of the particular type of fibrous material or stock being treated, as regards chlorine consumption, rate of reaction, and the like, and this may be determined for each particular fibrous material by tests.

The overflow outlet 120 from the chlorination chamber 115 discharges into a conven tional type of washing apparatus, shown diagrammatically as a worm-type drum wash-..

for spraying wash Water upon the stock.

The stock feeds into the interior of one end of the rotary drum and is carried continuously through by the spiral conveyor as it is washed by the sprays and discharges from the other end. A part of the water in-the stock drains through the perforated drum into a receiving tank 126 having a discharge pipe 127, so that the stock generally discharges from the washer at a consistency of about 10% to 12%. The short time of treatment in the chlorination chamber coupled with the fact that the free acid formed in the reaction is washed out immediately after chlorination further serves to prevent injury to the fibers. An additional spray pipe 128 is preferably provided to direct an alkaline liquor upon the chlorinated material upon the screen to neutralize any acid or free chlorine remaining in the fibrous mass, thereby avoiding the necessity for further acidproof apparatus, as well as assisting in dissolving out reaction products of the chlorination. If desired, an alkaline steeping may be given at this point, this being advantageous in the case of fibrous stock which is less defibered.

A discharge 130 from the worm washer feeds to a further thickening device where the stock is dewatered to a consistency of substantially 15% or higher, preferably 20% to 30%, to render it readily permeable to gas. A continuous centrifugal thickener functions very satisfactorily for this purpose, and such a machine is diagrammatically illustrated herein. This comprises an inner distributing rotor 131 having a spiral flange 132, the rotor being keyed to a shaft 133 driven by a motor 134, and a second rotor or perforated filtering screen 135 carried by a sleeve 136 rotatably mounted upon shaft 133 and also driven from motor 134 through gearing (not shown) at a speed which is preferably slightly less than the speed of the rotor 131. The outer screen is surrounded by a stationary annular casing or trough 138. The discharge 130 continuously feeds the stock into the space between the inner rotor 131 and the outer perforated filtering screen 135, where it is carried through the machine by the spiral flange 132 while being subjected to such centrifugal force as to cause a portion of the retained water in the mass to pass through the filtering screen 135 into the trough 138, from where the filtrate is removed by a pipe 139. Other well known types of continuous thickeners may be used for this purpose, such asrotary vacuum filters or cylindrical thickeners with pressure rolls to regulate the water content of the stock.

The dewatered stock discharged from the centrifugal machine is fed by a chute 140 to a supply trough 141 from-where it is scooped by an endless bucket elevator 142 and fed into a chlorination tower 143 constructed of acid and chlorine proof material where the second stage of the chlorination is effected. After the initial chlorination it is found that the fibers may be subjected to a strong or drastic chlorinating treatment with chlorine gas or bromine at high density or consistency without objectionable results. In this stage of more drastic action in which a hi h chlorine concentration is effective in the brous mass the chlorine gas reacts with the more resistant ligneous matter with consequent resolution of the shives or other undefibered material, this permitting the successful resolution of hard wood into satisfactory ulp. At the same time the strength of the hers is maintained, and other high quality characteristics are secured. During such reaction, the ligneous and other mate rial in the shives is apparently changed by the action of the chlorine gas into compounds which may thereafter be readily washed out with alkaline solutions, or which are of such character as to color and other characteristics as to be subsequently unobjectionable and ineffective to lower the quality of the resulting pulp.

As shown diagrammatically herein, the elevator 142 discharges into a hopper 145 which feeds into a screw conveyor 146 having an opening 147 on the lower side thereof opposite the open upper end of the tower 143. Stock feeds through the opening 147 into the upper end of the tower 143 as needed to maintain the tower full of stock, the surplus stock handled by the screw conveyor 146 being discharged at the end 148 and returned to the source of supply. The tower 143 is provided with an inlet 150 for the introduction of a controlled supply of chlorine gas, and controlled out-lets 151 and 152 for the discharge of gas. The gas discharging from. the tower which contains some freechlorine is preferably passed to recovery apparatus (not shown), such as a water absorption system, where chlorine water is formed which may be used in the first stage of the chlorination. Water or other slushing liquid is introduced adjacent the base of the tower at 154 to dilute and slush out-the pulp through the water sealed discharge 155 formed between the lower end 156 of the shell of the tower and a base 157, the stock passing into an annular trough 158. The stock passes from the upper end to the lower end of the tower by gravity in accordance with the rate at which it is slushed out at the bottom, thereby providing a continuous travel of dewatered stock through a controlled and maintained atmosphere of chlorine gas which thoroughly permeates the mass of fibers and effects intimate contact therewith. Generally a treating period of 15 to 30 minutes in this second stage is satisfactory, although a longer period may be used.

The chlorinated stock slushed out at the base of the tower 143 is discharged, with the aid of additional slushing liquid introduced into the trough 158 by a pipe 160, through a pipe 161 into a solvent tank 162. Here it is mixed with a cont-rolled quantity of alkali continuously supplied from a pie 163 having a control valve 164 for the purpose of dissolving out reaction products of the chlorination. The tank 162 is constructed to effect a continuous and uniform treatment of the fibrous material to secure a thorough mixing of the material with the solvent alkali. For this purpose the tank is provided with a plurality of staggered baffles 166 which provide a circuitous path for the flow of material from the inlet 167' to the discharge 168 connected to the suction side of a pump 169. The first compartment of the tank 162 is preferably provided with suitable agitating mechanism such as a driven shaft having a plurality of rotary stirring arms 171. The capacity of the tank 162 is such that the treated material is allowed to remain about half an hour therein, this giving sufficient time for soluble reaction products of the chlorination to be dissolved. Any suitable alkali may be used for this purpose, dilute cold solutions of caustic soda, sodium carbonate or sodium sulphite giving very satisfactory results.

The pump 169 feeds the diluted stock through a pipe to-a continuous filter mechanism indicated generally. at 176 which may be a conventional rotary vacuum filter, such as an Oliver filter, similar in construction to the filter 95. The dissolved reaction products of the chlorination and the excess alkaline liquor are washed out of the stock by wash water from spray pipes 177, and the filtered and thickened material is removed from the surface of the filter by ascraper 178 into achute 179 which discharges into the first tank 180 of a bleacher which is preferably of the continuous type. The alkaline liquor and wash water drawn by suction into the interior of the rotary screen 176 are discharged through a central pipe 182, and a portion of this alkaline liquor may be supplied to the supply pipe 128 of the worm washer.

Any suitable construction of continuous bleacher may be used. As shown, three connected tanks 180, 183 and 184, each having a rotary shaft 185 provided with stirring arms 186, are provided. The tanks are arranged at successively lower elevations and the bottom of a preceding tank is connected to the upper end of a succeeding tank by a pipe connection 187. Each connection 187 has its highest point located below the level of the stock in the preceding tank, whereby a head is effective to secure a flowthrough the pipe. The capacity of the tanks is such as to insure sufficient time for the completion of the "final bleaching action during the time the material flows through the bleaching tanks. A controlled quantity of suitable bleaching agent such as bleach liquor, sodium hypochlorite or chlorine water, is continuously added by a pipe 188 having a control valve 189. Due to the effective chlorination treatment which serves to further disintegrate and complete the pulping of the fibrous material, the quantity of bleach required is very materially reduced, approximately 1% to 3% of chlorine on the dry weight of the pulp being suflicient to produce a pulp having a high white color. The bleached pulp stock continuously discharged from the last tank 184: through pipe 190 IS forced by a pump 191 to a rotary vacuum filter indicated generally at 192, similar in construction to the filter 176, where the pulp is Washed and thickened. The bleached pulp is then discharged through chute 193 into a stock chest 194 where it is stored for further treatment or for use.

The cooking and chlorination treatments as carried out in accordance with this invention are s'o controlled or limited in their effects upon the cellulose content of the fibrous material, that eVen the less resistant beta and gamma celluloses are substantially unin 'ured, and only small amounts are lost by solution in contradistinction to the conventional pulping methods heretofore used. The alpha cel-- Iulose content is not materially hydrolyzed or converted into oxycellulose. The result is that a novel and superior white pulp product having unusually advantageous characteristics with a high yield is obtained. In actual tests using chestnut and gum, this pulp product has been found to contain in cellulose content in excess of 20% of beta and gamma cellulose and less than 80% of alpha cellulose. The average strength is more than 50% higher than thatof paper formed from conventional soda pulp from the same species of wood, often being twice as strong, and is superior to that of paper formed fromstrong sulphite pulp. The bleached product is of the highest color grade. The pulp is characterized by high felting and clay carrying qualities, and it may be loaded to contain as much as 40% of filler without dusting. Paper formed from the product is free of the objectionable fuzziness,.which is a characteristic of paper formed from soda pulp. The combination of high strength, good color and exceptional clay carrying qualities makes the product highly satisfactory for use in printing paper, such as book paper. The pulp is free, that is water drains rapidly through a mat undergoing formation on a forming wire, and is easily hydrated, which makes the pulp especially suitable for other types of high-grade paper, such as bonds and writing paper, parchment, glassine, waxing, and the like. The yield of unbleached pulp generally averages between 75% to 80% on the dry weight of the wood, while the yield of bleached pulp generally averages over 60% on the dry weight of the wood. This is an average increased yield of over 30% as compared to the soda process, and is materially higher than average yields obtained by the sulphite and kraft processes.

The following is a typical example of a pulping treatment carried out in accordance with this invention. To a charge of around 14,000 pounds of leached chestnut chips (dry basis), a cooking liquor, consisting of about 1800 pounds of sodium sulphite and 700 pounds of sodium bicarbonate (both calculated as sodium carbonate) in sufficient water to provide a concentration of about 8% to 12% sodium sulphite and 3% to 5% sodium bicarbonate, is added to the digester. The

-wood is preferably steamed for about half an hour before the cooking liquor is added.

The charge is then brought up to approximately 125 C. with steam, the cooking being continued at around this temperature for approximately two hours. The control of the neutrality of the cooking liquor is effected by the introduction of carbon dioxide gas through the pipe 30, or the relief of excess pressure through the pipe 32. The valve is then opened and the liquor in the digester is blown back into the receiving tank 23 where fresh liquor is added from tank 27 to bring it up to strength and volume for the treatment of a subsequent charge. The chips impregnated with the liquor are then steamed until the temperature is brought up to approximately 160 C. or higher, an excess of carbon dioxide gas being maintained. This second stage of the cooking is generally carried on from one to four hours. The cooked chips are then dumped into the dump tank and washed, the plug valve for the outlet being closed. The plug valve is then opened and the shaft 45 of the leach caster driven to feed the softened chips at a controlled rate to the rod mill 60. With a mill having a shell approximately 12 feet long and 6 feet in diameter and containing about 40,000 pounds of rods, a rate of feed of the chips diluted to a consistency of 5% to 8% to give a controlled output of about 13 tons to 18 tons of rod-milled stock in 24 hours is quite satisfactory. The material is then diluted, screened to remove undefibered lumps and knots, filtered, and then further diluted for the first stage chlorination.

Chlorine water containing approximately to 90% of the chlorine required for complete chlorination of the pulp is used. The chlorine is added to the stock in the form of solution in water containing approximately .2 to .47?) chlorine or is added directly as chlorine gas. In the former case the fibrous material is made down to a consistency of about 4% to 6%, the addition of the chlorine water bringing the consistency to about 1% to 4%. In the latter case the consistency of the material is made down initially to about 2% or even less. The rate of flow through the chlorination chamber 115 is controlled to give a treating time of about half an hour. The chlorinated stock is washed and given an alkaline treatment with cold dilute caustic soda, and then after being thickened to about 20% to 30% consistency is fed to the chlorinating tower 143. Here it is subjected to the second stage chlorination by passing through a maintained layer of chlorine gas for about 15 to 30 minutes. Both stages of the chlorination are carried on at ordinary room temperatures. The chlorinated stock is then introduced into the alkali solvent tank 162 with a sufficient quantity of cold .1% NaOH solution to render the mass distinctly alkaline and is agitated and steeped therein for about half an hour. After washing and making down to about 5% consistency, the material is introduced into the bleacher with a quantity of hypochlorite liquor suflicient to bring the consistency to about 4% to 5% and to provide about 1% chlorine 'onthe dry weight of the pulp. The flow of stock through the bleacher is controlled to provide a treating time of about one hour or more. A preliminary high density bleach may be given, if desired, before the stock is diluted. The bleached pulp is then washed and thickened and dropped to a stock chest where it is ready for use in the manufacture of high grade paper.

While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes-may be made in either without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In the manufacture of pulp from hard deciduous woods, such as chestnut, oak, gum and the like, the method which comprises cooking the hard woody fibrous material with cooking liquor including an alkali metal sulphite and the salt of a weakly ionized polybasic acid to effect a partial defibering of the fibrous material, then further disintegrating the fibrous material to pulp by treatment with a chlorinating agent, and then bleaching to produce a pulp suitable for the manufacture of higher class papers, such as for printing, writing and the like.

2. In the manufacture of pulp from fibrous material, the method which comprises cooking the fibrous material with cooking liquor including an alkali metal sulphite and the salt of a weakly ionized polybasic acid, diluting the cooked material to low consistency, subjecting the diluted material to the action of a chlorinating agent, the consistency of said diluted material being controlled to prevent during chlorination an objectionable temperature rise of the diluted mass, then raising the consistency of said chlorinated material, and subjecting said material of higher consistency to the action of a chlorinating agent.

3. In the manufacture of pulp from hard deciduous woods, such as chestnut, oak, gum and the like, the method which comprises subjecting the hard woody fibrous material to digestion with chemical cooking liquor, the conditions of the digestion treatment and the character of-the chemical cooking liquor being controlled to maintain substantial neutrality of the cooking liquor during the digestion and to effect only a partial defibering of the fibrous material, and then further disintegrating the fibrous material to pulp by treatment with a chlorinating agent.

ion

masses 4. In the manufacture of pulp from wood chips, such as chips of chestnut, oak, gum and the like, the method which comprises cooking the chips with chemical under such conditions of temperature and pressure and of concentration and character of chemical that the chips are only partially defibered and the cellulose is substantially unaffected and high strength is maintained, then mechanically disintegrating such as byrod milling the cooked material to break it up into small pieces but insufiicient to effect pulping, whereby small particles and hard fiber bundles of shives are directly exposed, then subjecting the mechanically disintegrated material to the action of a chlorinating agentto further disintegrate the hard fiber bundles and shives to pulp, washing out the reaction products of the chlorination, and bleaching the resultant pulp to produce a pulp suitable for the manufacture of higher class papers, such as for printing, writing and the like.

5. In the manufacture of pulp from fibrous material,the method which comprises cooking the fibrous material with a cooking liquor including a normal alkali metal sulphite and an alkali metal salt of a weakly ionlzed polybasic acid to effect. only a partial defibering of the material, mechanically disintegrating such as by rod' milling the cooked material to break it up into small pieces but insufficient to effect pulping, further disintegrating the fibrous material to pulp by treatment with a chlorinating agent, dissolving out reaction products of the chlorination, and bleaching the resultant pulp to produce a pulp suitable for the manufacture of higher class papers,

such as printing, writing and the like.

6. Apparatus of the character described comprising in combination, cooking means, means for introducing cooking liquor and fibrous material into said cooking means, a

mechanical disintegrator, means for introducing the cooked material discharged from said cooking means into said mechanical disintegrator, a chlorination chamber, and means for introducing the material discharged from said disintegrator and a chlorinatlng agent into said chlorination chamber to further disintegrate the fibrous material into its ultimate fibers, means for washing out the reaction products of the chlorination, and bleaching means for the resultant pulp.

7. Apparatus of the character described comprising in combination, cooking means for cooking fibrous material without substantial defibering thereof, means for draining the cooked material, means for transporting the drained material at high consistency, a mechanical disintegrator, means for introducing the transported material and dilution liquor into said mechanical disintegrator, a chlorination chamber, and means for introducing the material discharged from said disintegrator and a chlorinating agent into said chlorination chamber to further disintegrate the material into its ultimate fibers.

8. Apparatus of the character described comprising in combination, cooking means, means for introducing cooking liquor and fibrous material into said cooking means, a mechanical disintegrator such as a rod mill, means for introducing the cooked material into said rod mill, a chlorination chamber, means for introducing the rod milled material at low consistency and a chlorinating agent into said chlorination chamber, a thickener, means for introducing the chlorinated material into said thickener to raise the consistency thereof to render it permeable to gas, a chlorination tower, and means for introducing the thickened material and chlorine gas into said tower.

9. Apparatus of the character described comprising-in combination, cooking means, means for introducing cooking liquor and fibrous material into said cooking means, a mechanical disintegrator such as a rod mill, means for introducing the cooked material discharged from said cooking means into said mechanical disintegrator, a chlorination chamber, means for introducing the material discharged from said disintegrator and a chlorinating agent into said chlorination chamber to further disintegrate the material into pulp, a solvent tank, means for introducing the chlorinated material and alkali liquor into said solvent tank to dissolve out reaction products of the chlorination, and means for bleaching the resultant pulp.

10. In the manufacture of pulp from fibrous material, the method which comprises heating the fibrous material with cooking liquor, withdrawing unabsorbed liquor, cooking the material in the presence of retained liquor, the treatment being so controlled as to soften the fibrous material without pulping thereof and so that high strength of the material is maintained, mechanically disintegrating the softened material such as by rod milling to break it up into small pieces but sufiicient to effect only a partial pulping, and then subjecting the partially .pulped material to the action of a chlorinating agent to further disintegrate the fibrous material to pulp.

11. In the manufacture of pulp from fibrous material, the method which comprises cooking the fibrous material in a chemical cooking liquor, the conditions of the cooking treatment and the character of the chemical cooking liquor being controlled to maintain substantial neutrality of the cooking liquor during the cooking treatment and to soften the fibrous material without substantial pulping thereof, then subjecting the softened fibrous material to a mechanical treatment to further reduce the material to small pieces but sufiicient to effect only a partial pulping, and

then subjecting the mechanically treated incompletely pulped material to the action of a chlorinating agent to. further disintegrate the material to pulp.

12. In the manufacture of high grade pulp from hard wood such as chestnut, the method which comprises subjecting the wood in chip form to a cooking treatment with chemical under such conditions of temperature and pressure and of concentration and character of chemical that the chips are merely softened but not substantially pulped and high strength of the material is maintained, then subjecting the softened chips to a mechanical treatment to further reduce the same to small pieces but sufiicient to effect only a partial pulping and leave a substantial proportion of shives and unreduced fiber bundles in the mass, screening the resulting mechanically treated incompletely pulped material to remove larger pieces and knots while passing the smaller pieces or shives and unreduced fiber bundles, then subjecting the screened material to the action of a chlorinating agent to further disintegrate this material to pulp, and washing and bleaching the pulped material to produce a pulp suitable for the manufacture of higher class papers, such as for printing, writing and the like.

13. In the manufacture of pulp from fibrous material, the method which comprises cooking the material with a chemical cooking liquor under such conditions of temperature and pressure and of concentration and character of chemical that the fibrous material is softened without substantial pulping thereof, then continuously subjecting the softened material to a mechanical treatment to further reduce the material but sufiicient to efiect only a partial pulping thereof and leave a substantial proportion of shives and unreduced fiber bundles in the mass, and continuously treating the mechanically reduced incompletely pulped material with a chlorinating agent to further disintegrate the material to P 1 1: In the manufacture of pulp from fibrous material, the method which comprises cooking the fibrous material with a cooking liquor including sodium sulfite and a carbonate of sodium, diluting the cooked material to a consistency of less than 5%, subjecting the diluted material to the action of chlorine water, the consistency of the diluted material being controlled to prevent during the chlorination an objectionable temperature rise of said diluted mass, then dewaterin the material to a consistency of substantially 15% or higher to render it permeable to gas, subjecting the dewatered material to the action of chlorine gas, washing out reaction products of the chlorination, and bleaching the resulting pulp.

15. Apparatus of the character described,

comprising in combination, a cooking vessel,

means for introducing cooking liquor and fibrous material into said cooking vessel, a mechanical disintegrator, means for introducing the cooked material into said mechanical disintegrator, a screen, means for passing the material from said mechanical disintegrator to said screen to separate tailings from said material, and means for returning tailings to said mechanical disintegrator.

16. Apparatus of the character described,-

comprising in combination, a cooking vessel, means for introducingcooking liquor and fibrous material into said cooking vessel, a mechanical disintegrator, means for introducing the cooked material into said mechanical disintegrator, a screen, means for passing the material from said mechanical disintegrator to said screen to separate tailings from said material, a chlorination chamber, means for introducing the mechanically disintev eehtteteett ot somehow.

Patent No, 1,843,467., Granted Fehmaty 2, 1932, to

MEN theotmm ET AL.

it is hereby certified that error appears in the printed specificatiomot the above numbered patent requiring eot'reetimrt as follows: Page 9, line 14, claim 4, for "of" read or; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the ease in the Patent Office. a

Signed and sealed this ZZnd day of March, A. D. 1932 M. J. Moore, (Seal) Acting Commissioner of Patents. 

